The spinal column is a highly complex system of bones and connective tissues that provides support for the body and protects the delicate spinal cord and nerves. The spinal column includes a series of vertebrae stacked one on top of the other. Each vertebra includes a vertebral body including an inner or central portion of relatively weak cancellous bone and an outer portion of relatively strong cortical bone. An intervertebral disc is situated between each vertebral body to cushion and dampen compressive forces experienced by the spinal column. A vertebral canal, called the foramen, containing the spinal cord and nerves is located posterior to the vertebral bodies. In spite of the complexities, the spine is a highly flexible structure, capable of a high degree of curvature and twist in nearly every direction. For example, the kinematics of the spine normally includes flexion, extension, rotation and lateral bending.
There are many types of spinal column disorders including scoliosis (abnormal curvature and twisting of the spine), kyphosis (abnormal forward curvature of the spine, usually in the thoracic spine), excess lordosis (abnormal backward curvature of the spine, usually in the lumbar spine), spondylolisthesis (forward displacement of one vertebra over another, usually in a lumbar or cervical spine) and other disorders caused by abnormalities, disease, or trauma, such as ruptured or slipped discs, degenerative disc disease, fractured vertebra, and the like. Patients that suffer from such conditions usually experience extreme and debilitating pain as well as diminished range of motion and nerve function. These spinal disorders may also threaten the critical elements of the nervous system housed within the spinal column.
In some instances, a spinal stabilization system may be installed on a segment of the spinal column to stabilize a portion of the spinal column to treat a spinal disorder. One particular spinal stabilization technique includes immobilizing portions of the spine of a patient by using elongate members such as relatively rigid orthopedic spinal rods that run generally parallel to the spine on opposite sides of the spinous processes. Another technique utilizes less rigid elongate members to provide a more dynamic stabilization of the affected regions of the spine. One example of such a spinal stabilization system is the Dynesys® system available from, Zimmer Spine, Inc., of Minneapolis, Minn.
Installation of such systems may be accomplished, for example, by accessing the spine posterially and fastening hooks, bone screws, or other types of vertebral anchors to the pedicles or other bony structures of the appropriate vertebrae. The vertebral anchors may be generally placed in a quantity of two per vertebra, one on either side of the spinous processes, and serve as anchor points for the elongate members.
It may be desirable in some circumstances to provide a cross connector, such as a transverse connector, to bridge across the spinal column from a first assembly of vertebral anchors and associated elongate member to a second assembly of vertebral anchors and associated elongate member of the spinal stabilization system to provide additional stability to the spinal stabilization system. Accordingly, there exists a need to provide alternative transverse connector assemblies which may be coupled between first and second vertebral anchors of a spinal stabilization system.